There are several types of existing sensing devices for sensing and locating objects behind walls and other building surfaces. For example, U.S. Pat. No. 4,859,931 (Yamashita et al.) discloses an electronic detector comprising both a capacitive sensor and a magnetic field sensor. The capacitive sensor is provided to locate non-metallic objects behind a wall surface, and the magnetic field sensor is provided to locate metallic objects behind a wall surface. U.S. Pat. No. 5,438,266 (Tsang) discloses an instrument for locating buried conductors. The instrument utilizes a signal generator and a coil having a substantially vertical axis coil attuned to pick up odd and even harmonics of a fundamental frequency of a periodic test current, thereby allowing the accurate location of buried conductors. U.S. Pat. Nos. 5,352,974 and 5,619,128 (both to Heger) each disclose stud sensors which utilize capacitive sensors for locating studs hidden behind a wall or other structural surface.
Zircon Corporation markets a multifaceted stud finder device called the VideoScanner.TM. 5.0 Model No. 54014. This device detects wood, metal, and live electrical wires hidden behind walls, floors and ceilings having conventional cross-sections. The device has normal and deep scan settings in one mode and a metal setting in another mode. Thus, the device can be set to scan for studs using a normal or deep scan setting, or it can be set to scan for metal objects. With either mode--the normal/deep scan settings or the metal setting, the device is first calibrated. To calibrate the device for sensing hidden objects, the activation switch is pressed and held down, and a ready indicator will appear on an LCD once the device has been calibrated. The activation switch is held down during scanning of the device along the applicable surface. Once the device is calibrated, it may be scanned to locate hidden objects such as wood or metal studs in the normal and deep scan settings, or metal objects in the metal setting. The device is further provided with a portion which allows continuous AC voltage detection. It will detect either 110 or 220 volts AC present in a live electrical wire hidden behind the applicable building surface. Once the voltage has been detected, the device will display a flashing voltage icon.